Common treatments like salbutamol cause the lungs to release harmful
chemicals if taken too often - bringing on more attacks.

Professor Peter Bradding and colleagues found that when inhalers
are used frequently, the lungs lose their ability to stop the
release of the harmful chemical.

"When we exposed cells in the lab to the inhaler drugs over
a period of time they increased the release of lung chemicals
that bring on attacks," said Bradding.

"Despite their usefulness in rapidly relieving asthma, relievers
may cause asthma to worsen when used too frequently. Moreover,
they are not always as effective as predicted,"

The research has important consequences for individuals with
poorly controlled asthma and for those who rely too heavily on
relievers whilst not using their preventer medication regularly.

Prof Bradding, of Leicester University, said if the finding is
confirmed it could lead to the development of new treatment strategies
benefitting thousands of people.

There are 5.4 million people in the UK who suffer from asthma.

"Professor Bradding aims to understand why it is that people
who use their reliever inhalers too often, without using a preventer
inhaler, are putting themselves at risk of worse asthma symptoms.

Research at the University of Pittsburgh had previously shown
that the chemical reverses the protective effects of other drugs
which prevent asthma attacks from happening.

Asthma specialists said that this could explain why some sufferers
who use the inhalers frequently report a gradual deterioration
in their condition over several months.

One leading specialist, Dr Mark Aronica of the Cleveland Clinic
in Ohio, said: "The concern is that this chemical could build
up in patients who take the drug frequently. We need clinical
studies to find out whether this is the case."